General laminated cores for use in electric motors are formed by punching an electromagnetic steel sheet into a predetermined shape, laminating the punched sheets, and joining the sheets, for example, through welding or caulking. However, during the punching, strain may occur in the electromagnetic steel sheet. Once the strain occurs in the electromagnetic steel sheet, the iron loss increases and energy efficiency of the electric motor deteriorates. Thus, for example, as described in Patent Documents 1 to 3, annealing may be performed to remove the strain after the punched electromagnetic steel sheets are laminated and joined.